media: mc: entity: Fix minor issues in comments and documentation

Commit ae219872 ("media: mc: entity: Rewrite
media_pipeline_start()") incorrectly referred to entity instead of pad
in a comment, and forgot to update a second comment accordingly when
moving the pipe from entity to pad. Furthermore, it didn't properly
reflow the documentation text it updated.

Fix those small issues.

Fixes: ae219872 ("media: mc: entity: Rewrite media_pipeline_start()")
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>